Merge pull request libgit2#6020 from lolgear/refactoring/stdint_ifdef_condition_has_been_reverted

Stdint header condition has been reverted.

Author: ethomson

include/git2/stdint.h

@@ -29,9 +29,7 @@
 //
 ///////////////////////////////////////////////////////////////////////////////
 
-#ifndef _MSC_VER // [
-#error "Use this header only with Microsoft Visual C++ compilers!"
-#endif // _MSC_VER ]
+#ifdef _MSC_VER // [
 
 #ifndef _MSC_STDINT_H_ // [
 #define _MSC_STDINT_H_
@@ -245,3 +243,5 @@ typedef uint64_t  uintmax_t;
 
 
 #endif // _MSC_STDINT_H_ ]
+
+#endif // _MSC_VER ]